JP4078898B2 - Thermo-optic phase shifter and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermo-optical phase shifter that reduces power consumption and a method for manufacturing the same.
[0002]
[Prior art]
The increase in the number of channels in the optical communication field is rapidly promoted by the advent of wavelength division multiplexing (WDM) communication systems. Accordingly, in order to achieve functional control for each channel, for example, to make the power of each channel constant or to perform switching, the number of optical elements corresponding to the number of channels is required.
[0003]
For this reason, recently, there is an increasing need for small optical circuit components that can be applied to optical switches and the like and can be integrated at high density. Conventionally, single optical switches have already been realized, and matrix switches having a plurality of input / output ports using many of these optical switches have been put into practical use. As a technology for realizing an optical switch, a method of connecting an input port and an output port by mechanically moving them (for example, JP-A-9-5653), and rotating a movable mirror to tilt it to a predetermined angle. A method of connecting an input port and an output port (for example, Japanese Patent Laid-Open No. 2001-255474 and IEICE General Conference Proposal C-3-8 (2002) p. 140), a method of using a liquid crystal (for example, Japanese Patent Laid-Open No. 62-187826), various techniques such as a method of changing the connection between the input and output ports by controlling the reflection of light by means such as generating bubbles at the intersections of the waveguides that are cross-connected. Has been proposed.
[0004]
Among them, a planar lightwave circuit (PLC) type device using a thermo-optic phase shifter is extremely easy to manufacture and highly integrated because it can use semiconductor circuit manufacturing technology in its manufacturing process. It has the feature that it is advantageous for high functionality and large scale.
[0005]
Usually, the thermo-optic phase shifter is realized as follows. First, an optical waveguide composed of a clad layer and a core is fabricated on a substrate. Then, a metal thin film or the like is formed on the optical waveguide, processed into a thin line shape along the optical waveguide, and energized. When electric power is applied to the thin film from the outside, heat is generated by the electric resistance of the thin film, and it operates as a heater for the optical waveguide. The heat generated in the heater travels through the cladding layer of the optical waveguide and reaches the core. As a result, the refractive index of the portion of the optical waveguide heated by the heater increases, the effective waveguide length increases corresponding to the refractive index change amount and the waveguide length, and the phase of light at the output end shifts. The amount of phase shift can be arbitrarily controlled by adjusting the electric power supplied to the heater. When the optical waveguide is made of quartz glass, the refractive index temperature coefficient (dn / dT) of quartz glass is about 1 × 10.^-5(/ ° C.).
[0006]
Then, one optical waveguide is branched into two at the input end, at least one of them is connected to a thermo-optic phase shifter, and the optical waveguide branched into two at the output end is recombined, whereby the optical switch is Can be realized. For example, the output at the output end can be made zero by shifting the phases of the light guided through the two branched optical waveguides by half a wavelength. Further, if the phase is not shifted, the light as it is input can be output. Thereby, ON / OFF of the output can be controlled.
[0007]
However, when a plurality of thermo-optic phase shifters are arranged in one optical circuit to cope with the increase in the number of channels, if the power consumed by one thermo-optic phase shifter is large, the power consumption of the entire optical circuit Becomes extremely large. In a thermo-optic phase shifter that has been put to practical use so far, for example, when light having a wavelength of 1550 nm normally used for optical communication is guided, the power required to change the phase by a half wavelength is per channel. It was about 400 mW. Therefore, for example, if a switch using the above-described thermo-optic phase shifter is provided for each channel in order to control a 40-channel optical communication circuit, a maximum power of 40 × 400 mW = 16000 mW = 16 W is required. A thermo-optic phase shifter with a power consumption of about 40 mW per channel has been reported at the research level, but this is still too large for the high integration required for thermo-optic components. .
[0008]
In order to reduce the power consumption of the thermo-optic phase shifter, a method for changing the material forming the optical waveguide to a material having a large temperature coefficient of refractive index, for example, a method using a polymer in the waveguide has been proposed (for example, patents). No. 2848144, Y. Hida et al., IEEE Photon. Technol. Lett., Vol.5 (1993), pp.782-784, Proceedings of the IEICE General Conference C-3-10 (2002), p.142, etc.).
[0009]
In addition, a technology has been proposed in which the structure of the thermo-optic phase shifter is provided with a groove between the optical waveguides so that the heat generated in the heater does not escape to the outside (for example, the IEICE General Conference Proceedings). C-3-61 (2001) p.226, IEICE General Conference Proceedings C-3-64 (2001) p.229, Q. Lai et al. IEEE Photon. Technol. Lett. 1998) pp. 681-683). These documents describe that a desired temperature increase can be obtained with a small input power by providing a groove.
[0010]
Furthermore, in order to prevent the heat generated by the heater from escaping to the substrate, there is a method of increasing the thickness of the clad layer located under the core. Furthermore, in the thermo-optic phase shifter formed on the silicon substrate, in order to prevent the heat generated by the heater from escaping to the substrate, the substrate surface located below the optical waveguide is removed, and the optical waveguide is bridged. (For example, JP-A-1-158413, JP-A-5-34525, and JP-A-2001-2222034). Furthermore, the paper “A. Sugita et al. Trans. IEICE, Vol. E73 (1990) pp. 105-109” leaves a part of the silicon substrate located below the optical waveguide, and the optical waveguide is a silicon substrate. Also disclosed is a technique for supporting the column.
[0011]
Furthermore, in Japanese Patent No. 3152182, a silicon thin film is selectively formed on a quartz substrate, an under clad is formed so as to cover the silicon thin film, and a position corresponding to the upper portion of the silicon thin film on the under clad. A core is formed on the substrate, an over clad is formed so as to cover the core, an optical waveguide is formed, a heater is formed on the optical waveguide, and a groove reaching the silicon thin film is formed at a position sandwiching the optical waveguide. A technique for removing the silicon thin film through the groove is disclosed. As a result, a gap can be formed between the optical waveguide and the quartz substrate, and the power consumption of the thermo-optic phase shifter can be reduced.
[0012]
[Problems to be solved by the invention]
However, the conventional techniques described above have the following problems. When optical waveguides are formed of polymers, the polymers are highly hygroscopic and the film quality deteriorates due to the absorption of moisture during the manufacture and use of thermo-optic phase shifters, compared to optical waveguides formed of quartz glass. Thus, there is a problem that the propagation loss of light increases. It is also difficult to form a passivation film that protects the optical waveguide on the optical waveguide formed of a polymer. For this reason, the optical waveguide formed of the polymer is less stable and less reliable than the optical waveguide formed of quartz glass. Although a method of embedding a polymer in a part of an optical waveguide formed of quartz glass is also conceivable, there are problems such as a complicated manufacturing process, low reproducibility, and an increase in propagation loss generated at the interface between the quartz glass and the polymer. .
[0013]
Further, in the method of providing a groove between the optical waveguides, the heat generated from the heater arranged immediately above a certain optical waveguide can be prevented from being transmitted to other adjacent optical waveguides, but the heat of the heater can be prevented. Cannot be prevented, and the effect of reducing power consumption is small.
[0014]
Furthermore, the method of increasing the thickness of the cladding layer below the core has a problem that cracks are generated due to stress generated in the cladding layer during film formation. Further, there is a problem that the substrate is warped by this stress. Furthermore, this stress degrades the optical properties of the optical waveguide. Furthermore, since the film formation time becomes long, it is not suitable for mass production. For this reason, it is difficult in the process to form a thick cladding layer.
[0015]
Furthermore, in the technique for removing the surface of the silicon substrate located below the optical waveguide, a strong acid such as hydrofluoric acid is required as an etchant in order to etch the silicon substrate. When the silicon substrate is etched, the heater is covered and protected with a resist. However, this resist cannot withstand fluorinated nitric acid, and the heater is damaged by the etching. As described above, the method for etching a silicon substrate has a process problem. Also, by removing a part of the silicon substrate, the substrate itself for securing the strength of the thermo-optic phase shifter is weakened, resulting in a decrease in the mechanical strength of the element. There is. In addition, by etching the silicon substrate, the state of application of stress to the cladding layer changes and becomes unstable, and the mechanical strength and optical characteristics of the cladding layer itself constituting the optical waveguide deteriorate. is there. Furthermore, as described in the paper “A. Sugita et al. Trans. IEICE Vol. E73 (1990) pp. 105-109”, if a part of a silicon substrate is left as a support, silicon has thermal conductivity. Since it is high, the heat insulating effect of the optical waveguide is remarkably impaired, and the original purpose of reducing power consumption cannot be achieved.
[0016]
Furthermore, the technique disclosed in Japanese Patent No. 3152182, that is, a silicon thin film is selectively provided on the substrate, and the silicon thin film is etched in a later process, whereby a gap is formed between the substrate and the optical waveguide. The forming technique also has a problem that it is difficult to etch the silicon thin film. Further, since the under clad is formed so as to cover the selectively formed silicon thin film, the upper surface of the under clad is not flat, and the core, over clad, and heater layers can be formed on the under clad. There is a problem that it is difficult.
[0017]
The present invention has been made in view of such problems, and provides a thermo-optical phase shifter that is easy to manufacture, has good optical characteristics, strength, stability and reliability, and has low power consumption, and a method for manufacturing the same. For the purpose.
[0018]
[Means for Solving the Problems]
  A thermo-optic phase shifter according to the present invention is provided on a substrate and the substrate.A sacrificial layer and provided on the sacrificial layerThe phase of the light of the optical waveguide is generated by generating heat in a cladding layer, a core that is provided in the cladding layer in a straight line or a curved line and that constitutes an optical waveguide, and a region that includes an area directly above or immediately below the core. A heater to be changed,The sacrificial layer andA groove is formed in a region sandwiching at least a region immediately below the heater in the cladding layer, and the groove is sandwiched between the grooves.Sacrificial layerIs removed, and a gap of 4 μm or more connected to the groove is formed.
[0019]
In the present invention, the phase of light guided through the optical waveguide can be changed by heating the optical waveguide with a heater. At this time, a groove is formed in a region of the clad layer sandwiching at least a region immediately below the heater, and a gap of 4 μm or more connected to the groove is formed between the portion of the clad layer and the substrate. As a result, it is possible to suppress the heat generated by the heater from being directly transferred to the substrate via the cladding layer, and the heat insulation between the optical waveguide and the substrate is improved. Thereby, the temperature of the optical waveguide can be increased efficiently with a small amount of heating. In addition, since the portion between the grooves in the cladding layer is separated from the substrate, the stress applied to the optical waveguide is reduced, and deterioration of the optical characteristics can be prevented. Furthermore, by separating the optical waveguide from the surrounding clad layer by the groove, the stress applied to the optical waveguide can be remarkably reduced, and the deterioration of the optical characteristics due to the application of the stress can be suppressed. As a result, the optical characteristics of the thermo-optic phase shifter are improved and the power consumption is greatly reduced. As a result, a large number of thermo-optic phase shifters can be integrated on a large scale. Furthermore, since no polymer is used, stability and reliability are excellent, and manufacturing is easy. Furthermore, since there is no process for etching silicon with a strong acid such as hydrofluoric acid, the manufacture is easy.
[0020]
  Another thermo-optic phase shifter according to the present invention is provided on a substrate, a sacrificial layer formed on the substrate and a sacrificial material having an etching rate higher than that of the material forming the substrate, and the sacrificial layer. In a region including a cladding layer formed of a material having an etching rate lower than that of the sacrificial material, a core that is provided in a linear or curved shape in the cladding layer to form an optical waveguide, and a region directly above or directly below the core And a heater that changes the phase of light of the optical waveguide by generating heat, and a groove is formed in a region sandwiching at least a region immediately below the heater in the sacrificial layer and the clad layer,The sacrificial layer sandwiched between the grooves is removed by etching,A gap connected to the groove between the portion of the cladding layer between the groove and the substrateAnd a support portion that is locally provided in a part of the gap in the extending direction of the core and supports the clad layer portion sandwiched between the grooves with respect to the substrate.It is characterized by that.
[0021]
In the present invention, the phase of light guided through the optical waveguide can be changed by heating the optical waveguide with a heater. At this time, by forming a groove in a region sandwiching at least the region immediately below the heater in the cladding layer, and forming a gap connected to the groove between the portion of the cladding layer and the substrate, It is possible to suppress the heat generated by the heater from being directly transferred to the substrate through the cladding layer, and to efficiently raise the temperature of the optical waveguide layer with a small amount of heating. As a result, power consumption is greatly reduced and large-scale integration becomes possible.
[0022]
In addition, by forming a sacrificial layer over the entire surface of the substrate, the upper surface of the sacrificial layer becomes flat, the clad layer can be easily formed, and the optical characteristics of the optical waveguide are improved. Furthermore, the gap can be easily formed by selectively removing the sacrificial layer between the portion of the clad layer and the substrate through the groove. As a result, a thermo-optic phase shifter having excellent optical characteristics can be easily produced with high controllability and high yield. Further, the sacrificial layer and the clad layer can be continuously formed, and the manufacturing process can be greatly simplified. As a result, it is possible to reduce the manufacturing cost and increase the yield. In addition, by providing the sacrificial layer intermittently, the stress generated in the sacrificial layer can be sufficiently released, and high reliability and high reproducibility of the film forming process can be realized.
[0023]
Moreover, it may have a support | pillar part which is provided in a part of said clearance gap and supports the part between the said grooves in the said cladding layer with respect to the said board | substrate. Thereby, since the stress applied to the optical waveguide layer is reduced, it is possible to prevent deterioration of the optical characteristics. Furthermore, the strength of the optical waveguide can be secured, which is advantageous for high density integration.
[0024]
Furthermore, the support column may be formed of the sacrificial material. Accordingly, the column portion can be formed by stopping the step of etching the sacrificial layer in the middle without providing a special step for forming the column portion.
[0025]
Alternatively, the support portion may be formed of a material whose etching rate is lower than that of the sacrificial material. Thereby, compared to the case where the etching of the sacrificial layer is stopped halfway and the column part is left, the column part can be formed in a self-aligned manner, and the controllability and reproducibility of the production are improved. Variations in the shape of the are reduced. In addition, the power consumption of the thermo-optic phase shifter can be further reduced by forming the column portion with a material having a low thermal conductivity.
[0026]
Furthermore, it is preferable that the thermal conductivity of the sacrificial material is smaller than the thermal conductivity of the material forming the substrate. As a result, even if a part of the sacrificial layer is left in the lower region of the heater, the heat conductivity of the sacrificial layer is small, so that the heat generated by the heater can be prevented from being transferred to the substrate as much as possible. The temperature of the optical waveguide layer can be increased efficiently. As a result, power consumption in one thermo-optic phase shifter is greatly reduced, and large-scale integration is possible.
[0027]
Furthermore, it is preferable that the sacrificial material is a glass material containing phosphorus, and the material forming the cladding layer is a glass material containing boron and phosphorus. As a result, a sufficient etching rate difference by the BHF solution is obtained between the sacrificial layer and the clad layer, and the clad layer is not deteriorated in the sacrificial layer removal step, so that the manufacturing process has high reliability and good reproduction. In addition, it is possible to realize a thermo-optic phase shifter with small propagation loss and excellent optical characteristics.
[0028]
  Furthermore, SupportBy making the thermal conductivity of the column portion smaller than that of the substrate, a path through which heat escapes from the heater to the substrate side is substantially reduced as compared with the case where the substrate is supported as described in the above-described conventional technology. Therefore, the power consumption can be greatly reduced.
[0029]
Or the said support | pillar part may be formed in a part of the direction where the said core extends in the area directly under the said core. As a result, the optical waveguide part where the heater is installed can be separated from the surrounding clad layer, and the stress can be released to the maximum to suppress the deterioration of optical characteristics, and a part of this optical waveguide can be supported from the substrate side. Therefore, the mechanical strength can be ensured. Furthermore, since the portions other than the support portions have extremely high heat insulation properties, power consumption can be greatly reduced, and large-scale integration of thermo-optical components can be achieved.
[0030]
Furthermore, it is preferable to have a support beam provided so as to stretch the groove and supporting a portion between the grooves in the cladding layer with respect to a portion sandwiching the groove together with this portion. As a result, the stress applied to the optical waveguide can be released as much as possible, the strength of the optical waveguide is improved, and it can be used in an environment subject to strong mechanical vibration. Although the power consumption is somewhat increased by providing the support beam, since the sacrificial layer below the support beam is removed, heat is prevented from escaping from the optical waveguide to the substrate via the support beam. A sufficient power consumption reduction effect can be obtained.
[0031]
Furthermore, of the side surfaces parallel to the direction in which the core extends in the groove, the side surface closer to the core is separated from the core at the end in the direction in which the core extends, as the end in the direction is approached. It is preferably curved. As a result, the most mechanically weak part corresponding to the base part of the bridge-shaped optical waveguide can be reinforced without changing the manufacturing process at all, thereby further improving the reliability of the thermo-optic phase shifter. be able to.
[0032]
Furthermore, the heater may be provided on the surface of the clad layer. Thereby, the heat generated from the heater can be prevented from escaping directly to the substrate without contributing to the temperature rise of the optical waveguide, and the heating efficiency of the optical waveguide can be improved. Further, the manufacturing process of the thermo-optic phase shifter is simplified, and high yield can be realized.
[0033]
Alternatively, the heater may be provided in the cladding layer. This prevents the heater from being exposed to the air, stabilizes it, and prevents the heater from being deformed or altered by the etching solution during fabrication, creating a highly reliable thermo-optic phase shifter. It becomes possible to do.
[0034]
Furthermore, it is preferable that the core and the cladding layer are made of a glass material containing quartz. As a result, it is possible to realize a thermo-optic phase shifter with small propagation loss of the optical waveguide and excellent optical characteristics and stability.
[0035]
Furthermore, it is preferable that the substrate is made of a glass material containing quartz or silicon. Thereby, the thermo-optic phase shifter of the present invention can be manufactured using a silicon semiconductor process. For this reason, the production of the thermo-optic phase shifter is facilitated, and the production reliability and reproducibility can be improved.
[0036]
  The method of manufacturing a thermo-optic phase shifter according to the present invention includes a step of forming a sacrificial layer on a substrate with a sacrificial material having an etching rate higher than that of the material forming the substrate, and etching on the sacrificial layer than the sacrificial material. A step of forming the lower clad layer with a material having a low speed, a step of forming a core extending linearly or curvedly on the lower clad layer, and an etching rate lower than that of the sacrificial material so as to cover the core The phase of the light of the optical waveguide composed of the lower clad layer, the core, and the upper clad layer is generated by generating heat in a region including the region directly above the core on the upper clad layer, and forming the upper clad layer with a material. A step of forming a heater to be changed, and the sacrificial layer or the sacrificial layer in a region sandwiching a region immediately below the heater in the upper cladding layer and the lower cladding layer. Forming a groove reaching the substrate, and etching the sacrificial layer located between the portion of the lower cladding layer between the grooves and the substrate through the groove to remove the lower cladding Forming a gap connected to the groove between a portion of the layer between the groove and the substrate;In addition, a strut portion is provided locally to support the clad layer portion sandwiched between the grooves with respect to the substrate in a part of the gap in the extending direction of the core.And a process.
[0037]
  Another method of manufacturing a thermo-optic phase shifter according to the present invention includes a substrateaboveForming a sacrificial layer with a sacrificial material having an etching rate higher than that of the material forming the substrate, and forming a first lower cladding layer on the sacrificial layer with a material having an etching rate lower than that of the sacrificial material A step of forming a heater on the first lower cladding layer, a step of forming a second lower cladding layer on the heater with a material having an etching rate smaller than that of the sacrificial material, and the second Forming a core extending linearly or in a curved line in a region including the region directly above the heater on the lower cladding layer, and forming the upper cladding layer with a material having an etching rate lower than that of the sacrificial material so as to cover the core. A step of forming, a region immediately above the heater in the upper clad layer and the second lower clad layer, and a front in the first lower clad layer. A step of forming a groove reaching the sacrificial layer or the substrate in a region sandwiching a region directly under the heater, and a position between the portion of the first lower cladding layer between the groove and the substrate through the groove; Etching the sacrificial layer to form a gap connected to the groove between a portion of the first lower cladding layer between the groove and the substrate; and the upper cladding layer and Forming a via connected to the heater in the second lower cladding layer.
[0038]
  Still another method for manufacturing a thermo-optic phase shifter according to the present invention includes a step of selectively forming a sacrificial layer having a thickness of 4 μm or more on a substrate with a sacrificial material having an etching rate higher than that of the material for forming the substrate. Forming a lower clad layer on the sacrificial layer with a material having an etching rate lower than that of the sacrificial material, and extending linearly or in a curved line to a region including the upper region of the sacrificial layer on the lower clad layer A step of forming a core, a step of forming an upper cladding layer with a material having an etching rate lower than that of the sacrificial material so as to cover the core, and heat generation in a region including the region directly above the core on the upper cladding layer Forming a heater for changing the phase of light in the optical waveguide comprising the lower clad layer, the core and the upper clad layer, and the upper clad And a step of forming a groove reaching the sacrificial layer or the substrate in a region sandwiching a region immediately below the heater in the lower clad layer, and removing the sacrificial layer by etching through the groove, the lower clad layer A gap of 4 μm or more connected to the groove is formed between a portion between the grooves in the substrate and the substrate.In addition, a strut portion is provided locally to support the clad layer portion sandwiched between the grooves with respect to the substrate in a part of the gap in the extending direction of the core.And a process.
[0039]
Still another method for manufacturing a thermo-optic phase shifter according to the present invention includes a step of selectively forming a sacrificial layer having a thickness of 4 μm or more on a substrate with a sacrificial material having an etching rate higher than that of the material for forming the substrate. A step of forming a first lower cladding layer on the sacrificial layer with a material having an etching rate lower than that of the sacrificial material, and a region including a region directly above the sacrificial layer on the first lower cladding layer. Forming a heater; forming a second lower cladding layer on the heater with a material having an etching rate lower than that of the sacrificial material; and a region immediately above the heater on the second lower cladding layer Forming a linear or curved core in a region including the upper cladding layer and a material having an etching rate lower than that of the sacrificial material so as to cover the core And a groove reaching the sacrificial layer or the substrate in a region directly above the heater in the upper cladding layer and the second lower cladding layer and a region sandwiching the region immediately below the heater in the first lower cladding layer. A step of forming and removing the sacrificial layer by etching through the groove, and having a thickness of 4 μm or more connected to the groove between the portion of the first lower cladding layer between the groove and the substrate. Forming a gap; and forming a via connected to the heater in the upper clad layer and the second lower clad layer.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, a first embodiment of the present invention will be described. FIG. 1A is a plan view showing a thermo-optic phase shifter according to the present embodiment, and FIG. 1B is a cross-sectional view taken along line A1-A1 ′ shown in FIG. 2A to 2D are cross-sectional views showing the method of manufacturing the thermo-optic phase shifter according to this embodiment in the order of the steps.
[0041]
As shown in FIGS. 1A and 1B, in the thermo-optic phase shifter according to the present embodiment, a substrate 1 made of, for example, silicon and having a thickness of 0.8 mm is provided. Layer 2 is provided. The sacrificial layer 2 is formed of, for example, phosphorus-added silica glass (PSG) in which phosphorus is doped into glass, and the film thickness thereof is, for example, 5 μm. A cladding layer 13 is provided on the sacrificial layer 2. The clad layer 13 includes a lower clad layer 3 provided on the sacrificial layer 2 and an upper clad layer 5 provided on the lower clad layer 3. The lower cladding layer 3 and the upper cladding layer 5 are made of, for example, BPSG doped with boron and phosphorus in glass, and the film thicknesses thereof are, for example, 14 μm and 15 μm, respectively. The substrate 1 may be formed of a semiconductor other than silicon or an insulator such as quartz glass. The sacrificial layer 2 is not limited to PSG, and may be formed of a material having an etching rate higher than that of the substrate 1 and the cladding layer 13 and capable of selective etching with respect to the substrate 1 and the cladding layer 13. As long as it satisfies, it may be formed of, for example, a glass other than a semiconductor or PSG.
[0042]
A core 4 extending in a direction parallel to the surface of the substrate 1 is provided on the lower clad layer 3, and an upper clad layer 5 is provided so as to cover the core 4. An optical waveguide 14 is formed by the core 4 and the cladding layer 13 around the core 4. The shape of the cross section perpendicular to the longitudinal direction of the core 4 is a rectangle having a height of, for example, 5.5 μm and a width of, for example, 5.5 μm. The core 4 is made of a material having a refractive index higher than that of the cladding layer 13, for example, GPSG (germanium / phosphorus-added silica glass), and the relative refractive index difference Δ between the core 4 and the cladding layer 13 is, for example, 0.8. 65%.
[0043]
Further, a thin film heater 6 is provided on the optical waveguide 14, that is, on the surface of the upper cladding layer 5. The thin film heater 6 is a thin film made of chromium, for example, and has a film thickness of 0.2 μm, for example. The thin film heater 6 includes electrode portions 6a at both ends and a heater portion 6b between the electrode portions 6a. The shape of the electrode portion 6a is, for example, a square, and the shape of the heater portion 6b is a thin line having a width of, for example, 10 μm and a length of, for example, 4 mm.
[0044]
  Furthermore, the region corresponding to the lower part of the thin film heater 6 in the cladding layer 13 and the sacrificial layer 2.Out ofBoth sides of the optical waveguide 14Area located atA groove 8 extending in parallel with the direction in which the core 4 extends is formed. That is, the groove 8 is formed in two places so as to sandwich the optical waveguide 14. The length of the groove 8 in the longitudinal direction, that is, the direction in which the core 4 extends is, for example, 4 mm, and the width of the groove 8, that is, the length in the direction orthogonal to the direction in which the core 4 extends is, for example, 250 μm. For example, the thickness is 29 μm. The distance between the grooves 8, that is, the ridge width of the optical waveguide 14 is, for example, 25 μm. Furthermore, the sacrificial layer 2 is removed and a gap 15 is formed between the optical waveguide 14 and the substrate 1. The height of the gap 15 is equal to the film thickness of the sacrificial layer 2 and is, for example, 5 μm. Thus, the optical waveguide 14 is separated from the cladding layer 13 other than the optical waveguide 14, the sacrificial layer 2, and the substrate 1 by the two grooves 8 and the gap 15, and has a bridge shape. The sacrificial layer 2 is formed on the entire surface of the substrate 1 except for the gap 15.The
[0045]
Next, a manufacturing method of the thermo-optic phase shifter according to the present embodiment will be described. First, as shown in FIG. 2A, a sacrificial layer 2 is formed on a substrate 1 made of, for example, silicon and having a thickness of, for example, 0.8 mm by an atmospheric pressure chemical vapor deposition method (AP-CVD). Make it. The material for forming the sacrificial layer 2 may be any material that can be selectively etched with respect to the substrate 1 and the clad layer 13. For example, it may be a semiconductor or glass, but in this embodiment, it is PSG. The film thickness of the sacrificial layer 2 is, for example, 5 μm. Next, a glass film mainly composed of quartz, for example, BPSG, is formed to a thickness of, for example, 14 μm by AP-CVD, and the lower cladding layer 3 is formed. The PSG for forming the sacrificial layer 2 and the BPSG for forming the lower clad layer 3 can be continuously formed by AP-CVD by changing the doping element in the middle.
[0046]
Then, a thin film 4 a is formed on the lower clad layer 3 with a material having a refractive index larger than that of the lower clad layer 3. The thin film 4a is made of, for example, GPSG (germanium / phosphorus-doped silica glass) in which the mixing amount of germanium and phosphorus is adjusted so that the relative refractive index difference Δ with the lower cladding layer 3 is 0.65%. A film is formed to a thickness of, for example, 5.5 μm by CVD.
[0047]
Next, as shown in FIG. 2B, the thin film 4a is patterned by photolithography and reactive ion etching (RIE) to extend in a direction parallel to the surface of the substrate 1, and a cross section orthogonal to this direction is rectangular. The core 4 having a shape is formed. The width of the core 4 is, for example, 5.5 μm. Next, an upper cladding layer 5 made of, for example, BPSG is formed to a thickness of, for example, 15 μm so as to embed the core 4, thereby producing an embedded optical waveguide.
[0048]
Next, as shown in FIG. 2C, a metal film such as a chromium thin film is formed to a thickness of, for example, 0.2 μm, for example, by an electron beam evaporation method in a region immediately above the core 4 on the surface of the upper cladding layer 5. To do. Then, the thin film heater 6 is formed by patterning into a predetermined shape by photolithography and wet etching.
[0049]
  Thereafter, as shown in FIG. 2D, a resist 7 is formed so as to cover the upper cladding layer 5 and the thin film heater 6. In the resist 7, two openings 7a are formed on both sides of the thin film heater 6 by photolithography. The distance between the openings 7a is, for example, 25 μm. Then, etching is performed by RIE using the resist 7 as a mask, and regions corresponding to both sides of the thin film heater 6 in the cladding layer 13 and the sacrificial layer 2 are selectively removed, and a groove 8 having a depth reaching the substrate 1 is formed. .The groove 8 may be formed so as to reach the sacrificial layer 2.
[0050]
Then, as shown in FIG. 1B, wet etching of the sacrificial layer 2 is performed with a buffered hydrogen fluoride solution (BHF) through the groove 8 while leaving the resist 7 in order to protect the thin film heater 6. The sacrificial layer 2 located below the optical waveguide 14 is removed. As a result, a gap 15 is formed in a region between the substrate 1 and the cladding layer 13 between the grooves 8. The height of the gap 15 is equal to the film thickness of the sacrificial layer 2 and is, for example, 5 μm. At this time, when a buffered hydrogen fluoride solution (BHF) is used as the etching solution, the etching rate for PSG, which is the material of the sacrificial layer 2, is about 6 to 10 times the etching rate for BPSG, which is the material for the cladding layer 13. It becomes. Also, silicon that is the material of the substrate 1 is hardly etched. For this reason, the PSG film functions as a sacrificial layer. In this manner, the thermo-optic phase shifter of this example can be manufactured.
[0051]
Next, the operation of the thermo-optic phase shifter according to this embodiment will be described. Electric power is supplied to the thin film heater 6 by an external power source (not shown). As a result, the thin film heater 6 generates heat and raises the temperature of the optical waveguide 14 to change its refractive index, thereby changing the effective length of the optical waveguide 14. As a result, the phase at the output end (not shown) of the light incident on the optical waveguide 14 from the input end (not shown) can be changed.
[0052]
In this embodiment, since the optical waveguide 14 is separated from the substrate 1 and the cladding layer 13 other than the optical waveguide 14, the heat generated by the thin film heater 6 can be prevented from escaping to the substrate 1 and the cladding layer 13. The waveguide 14 can be efficiently heated. Note that the heat generated in the thin film heater 6 escapes somewhat through the longitudinal direction of the clad layer 13 and the air filled in the grooves 8 and the gaps 15. However, in the structure of the thermo-optic phase shifter of this embodiment, the heat is generated. Because there are few heat conduction paths, the amount of heat that escapes is extremely small. Therefore, the optical waveguide 14 can be efficiently heated. For this reason, the power consumption accompanying the driving of the thermo-optic phase shifter is extremely small.
[0053]
As the distance between the substrate 1 and the optical waveguide 14, that is, the gap 15 is increased, the heat insulating property of the optical waveguide 14 is improved and the power consumption of the thermo-optic phase shifter is reduced. By setting the height of the gap 15, that is, the thickness of the sacrificial layer 2 to 4 μm or more, the power consumption of the thermo-optic phase shifter can be further reduced by half to 20 mW or less from the conventional minimum value of 40 mW. For this reason, the gap 15 is preferably 4 μm or more.
[0054]
In this example, when light having a wavelength of 1550 nm was used as incident light, the amount of power required to make the phase shift amount half a wavelength was measured to be about 10 mW. This is an extremely small value corresponding to 1/40 of the power consumption of the conventional thermo-optic phase shifter. That is, when a 40-channel optical switch is manufactured by the thermo-optic phase shifter of this embodiment, this optical switch can be controlled with power for one channel of the optical switch by a normal thermo-optic phase shifter. Along with this, it is possible to reduce the size of the external package, such as simplification of the power supply circuit, and the device can be further reduced in size and scale.
[0055]
In this embodiment, since the optical waveguide 14 is separated from the substrate 1 and the cladding layer 13, the stress applied from the substrate 1 and the cladding layer 13 is small. Further, since the sacrificial layer 2 is as thin as about 5 μm, the stress acting on the optical waveguide 14 from the sacrificial layer 2 is small. Furthermore, since the substrate 1 is not etched, the stress applied from the substrate 1 to the optical waveguide 14 does not change according to the etching amount, and the substrate 1 does not become brittle by etching. Furthermore, since the sacrificial layer 2 is formed on the entire surface of the substrate 1 when the lower clad layer 3 is formed, the surface of the lower clad layer 3 becomes flat, and the core 4 is formed on the flat surface. Can be formed. For this reason, the thermo-optic phase shifter according to the present embodiment has less polarization dependency due to stress, good optical characteristics, and high mechanical strength. Furthermore, since the thermo-optic phase shifter of this example does not use a polymer as its material, it has high heat resistance and excellent stability and reliability.
[0056]
The thermo-optic phase shifter according to the present embodiment is not damaged in the optical characteristics as compared with the conventional thermo-optic phase shifter, and a temperature (input power) at which a phase shift amount three times the wavelength can be obtained. It was confirmed that even when heated to about 60 mW, no breakage or the like due to thermal stress occurred and the mechanical strength was not a problem.
[0057]
Furthermore, in this embodiment, since there is no step of etching silicon, it is not necessary to use a strong acid such as hydrofluoric acid as an etching solution. Further, as described above, since the sacrificial layer 2 is formed on the entire surface of the substrate 1, no step is formed on the surface of the lower cladding layer 3, and the surface is flat. Further, the resist 7 provided for forming the groove 8 can be used as it is as the protective film of the thin film heater 6 after the groove 8 is formed. Thereby, it is not necessary to newly form a resist after the grooves 8 are formed. Furthermore, since no polymer is used as the material of the thermo-optic phase shifter, there is no restriction on annealing. For this reason, the thermo-optic phase shifter according to the present embodiment is easy to manufacture. The manufacturing method of the thermo-optical phase shifter according to the present embodiment has very little changes from the conventional manufacturing method of the thermo-optical phase shifter, and it is not necessary to introduce a new etching apparatus or the like. Further, there is no process with a high load that causes a decrease in yield, and it can be immediately applied to any optical waveguide.
[0058]
Next, a second embodiment of the present invention will be described. FIG. 3A is a plan view showing the thermo-optic phase shifter according to the present embodiment, and FIG. 3B is a cross-sectional view taken along line A2-A2 ′ shown in FIG. Since the configuration and manufacturing method of the optical waveguide 14, the thin film heater 6, and the groove 8 in this embodiment are the same as those in the first embodiment, detailed description thereof is omitted. The feature of the second embodiment is that the sacrificial layer 2 under the thin film heater 6 is all removed by etching in the first embodiment, but in this embodiment, a part of the sacrificial layer 2 is left and the column 2a. It is in having formed. The width of the sacrificial layer 2 (support 2a) to be left can be controlled by the etching time by clarifying the etching rate in advance.
[0059]
When the thermo-optical phase shifter is subjected to mechanical stress such as extremely strong vibration, the structure of the optical waveguide 14 in the first embodiment is the same as that of the suspension bridge, so that the optical waveguide 14 may break in some cases. There is. Even if the optical waveguide 14 is not broken, the optical waveguide 14 may be curved and come into contact with the substrate 1 or the clad layer 13 other than the optical waveguide 14, which may reduce the thermal efficiency and increase the power consumption. In order to support the optical waveguide 14, Japanese Patent Application Laid-Open No. 1-158413 discloses a method of stopping etching of a silicon substrate halfway. However, if a support is formed of a material having high thermal conductivity such as silicon, consumption is reduced. There arises a problem that the power is remarkably increased. Thus, there is a trade-off between securing strength and reducing power consumption. On the other hand, as in the present embodiment, the sacrificial layer 2 is made of PSG or the like having low thermal conductivity, and a part of the sacrificial layer 2 located immediately below the optical waveguide 14 is left to form the support 2a. By doing so, it is possible to significantly reduce power consumption as compared with the case where the support column is formed of silicon or the like having high thermal conductivity.
[0060]
The power consumption of the thermo-optic phase shifter according to the present embodiment varies greatly depending on the width of the sacrificial layer 2 that remains, that is, the support column 2a. When the width of the support 2a was 5 μm and 10 μm, the power consumption at which a phase shift amount corresponding to a half wavelength with respect to light having a wavelength of 1550 nm was measured, and as a result, they were about 60 mW and about 120 mW, respectively. Therefore, the power consumption can be sufficiently achieved as compared with the conventional thermo-optic phase shifter. In addition, as compared with the case where the optical waveguide is completely separated from the substrate as in the first embodiment, 6 to 12 times as much power is required. However, in terms of mechanical strength, the thermo-optic phase shifter according to this embodiment is superior to the thermo-optic phase shifter according to the first embodiment. Therefore, the thermo-optic phase shifter according to the first embodiment and the thermo-optic phase shifter according to this embodiment may be selected according to the application.
[0061]
Next, a third embodiment of the present invention will be described. 4A to 4D are cross-sectional views showing the method of manufacturing the thermo-optic phase shifter according to this embodiment in the order of the steps. FIG. 5A is a plan view showing the thermo-optic phase shifter according to the present embodiment, and FIG. 5B is a cross-sectional view taken along line A3-A3 ′ shown in FIG. In the first embodiment, the sacrificial layer 2 is formed on the entire surface of the substrate 1 and the sacrificial layer 2 and the lower cladding layer 3 are continuously formed. In this embodiment, the sacrificial layer 2 is formed. It is characterized in that it is provided only in a region corresponding to the lower part of the thin film heater 6.
[0062]
Depending on the material for forming the sacrificial layer 2, an extremely large stress is generated by forming the sacrificial layer 2 on the entire surface of the substrate 1. For this reason, the optical characteristics of the optical waveguide 14 may be degraded, and film formation defects may occur in the formation of the optical waveguide. For this reason, in this embodiment, only the sacrificial layer 2 is first formed, and then patterned so that the sacrificial layer 2 remains only in the necessary portions.
[0063]
First, as shown in FIG. 4A, a sacrificial layer 2 is formed on the entire surface of the substrate 1. Then, the sacrificial layer 2 is patterned and selectively removed by photolithography and RIE. At this time, since the sacrificial layer 2 remains only under the thin film heater 6 and becomes a thin line, the film stress is released. As the material of the sacrificial layer 2, for example, PSG is used as in the first embodiment.
[0064]
Next, as shown in FIG. 4B, a lower clad layer 3, a core 4 and an upper clad layer 5 are formed on the sacrificial layer 2 by the same method as in the first embodiment. Next, as shown in FIG. 4C, a thin film heater 6 is formed in a region corresponding to the upper side of the sacrificial layer 2 on the surface of the upper cladding layer 5. Next, as shown in FIG. 4D, a resist 7 is formed on the upper cladding layer 5 and the thin film heater 6 as in the first embodiment described above. Then, the upper cladding layer 5, the lower cladding layer 3, and the sacrificial layer 2 are sequentially etched using the resist 7 as a mask, thereby forming etching grooves 8 on both sides of the optical waveguide 14.
[0065]
Thereafter, as shown in FIGS. 5A and 5B, the sacrificial layer 2 (see FIG. 4D) is wet-etched through the grooves 8 to remove the sacrificial layer 2. Thereby, the sacrificial layer 2 does not remain, and a thermo-optic phase shifter in which the lower clad layer 3 is provided on the substrate 1 can be manufactured outside the groove 8. The configuration and manufacturing method other than those described above in the present embodiment are the same as those in the first embodiment described above.
[0066]
In this embodiment, since the sacrificial layer is selectively etched, the process is increased by one step, but the stress generated in the sacrificial layer can be released. For this reason, the polarization dependence of the optical waveguide 14 can be further reduced, and the optical characteristics are further improved. Further, by patterning the sacrificial layer 2 in advance, there is no variation in etching when the sacrificial layer 2 is removed by wet etching, and it is possible to further improve the reliability and yield.
[0067]
Furthermore, BHF can be used as an etching solution by forming the sacrificial layer 2 by PSG. For this reason, as described in the above-mentioned Japanese Patent No. 3152182, it is not necessary to form a sacrificial layer with silicon and use hydrofluoric acid as an etching solution. For this reason, the thermo-optic phase shifter according to the present embodiment is easier to manufacture than the thermo-optic phase shifter described in Japanese Patent No. 3152182.
[0068]
Next, a fourth embodiment of the present invention will be described. FIG. 6A is a plan view showing the thermo-optic phase shifter according to the present embodiment, and FIG. 6B is a cross-sectional view taken along line A4-A4 ′ shown in FIG. This embodiment is an embodiment in which the second embodiment and the third embodiment are combined. As shown in FIGS. 6A and 6B, in this embodiment, the method for manufacturing the sacrificial layer 2 (see FIG. 4D) and the optical waveguide 14 is the same as that in the third embodiment. The feature of this embodiment is that the column 2a is formed while leaving a part of the sacrificial layer 2. The width of the sacrificial layer 2 to be left can be controlled by adjusting the etching time by clarifying the etching rate in advance. The reason for forming the support 2a is as described in the second embodiment, and the effect of reducing the power consumption is reduced, but the strength can be improved. For this reason, when a large mechanical strength is indispensable for the thermo-optic phase shifter, it can be used in place of the thermo-optic phase shifter according to the third embodiment described above. It is possible to balance power consumption.
[0069]
Next, a fifth embodiment of the present invention will be described. FIG. 7A is a plan view showing the thermo-optic phase shifter according to the present embodiment, and FIG. 7B is a cross-sectional view taken along line A5-A5 ′ shown in FIG. FIGS. 8A to 8D are cross-sectional views showing the manufacturing method of the thermo-optic phase shifter according to this embodiment in the order of steps. In the first embodiment described above, the thin film heater 6 is formed on the surface of the upper clad layer 5, but in this embodiment, the thin film heater 6 is formed inside the lower clad layer 3. That is, the first lower clad layer 9 in which the lower clad layer 3 is formed on the sacrificial layer 2 and the second lower clad layer 10 formed on the first lower clad layer 9. The thin film heater 6 is formed on the first lower clad layer 9, and the second lower clad layer 10 is formed so as to embed the thin film heater 6. The second lower clad layer 10 and upper clad layer 5 are provided with vias 11 for supplying electric power to the electrode portion 6 a of the thin film heater 6.
[0070]
Next, a manufacturing method of the thermo-optic phase shifter according to the present embodiment will be described. First, as shown in FIG. 8A, after the sacrificial layer 2 is formed on the substrate 1, a first lower clad layer 9 is formed, and a chromium film as a material for the thin film heater 6 is formed. Patterning. Next, as shown in FIG. 8B, the second lower cladding layer 10 is formed, the thin film heater 6 is embedded, and the thin film 4 a that is the material of the core 4 is formed. Next, as shown in FIG. 8C, the thin film 4a is patterned to form the core 4, and the upper cladding layer 5 is formed. Next, as shown in FIG. 8D, a groove 8 is formed and the sacrificial layer 2 is etched. Then, electrode vias 11 connected to the thin film heater 6 are formed in the upper clad layer 5 and the second lower clad layer 10. The electrode via 11 is formed by photolithography and RIE. Thereby, a thermo-optic phase shifter as shown in FIGS. 7A and 7B can be manufactured. The configuration and manufacturing method other than those described above in the present embodiment are the same as those in the first embodiment described above.
[0071]
In each of the first to fourth embodiments described above, the resist 7 (see FIG. 2D) used when forming the groove 8 is left after the groove 8 is formed, and the sacrificial layer 2 is formed. It is used to protect the thin film heater 6 during etching. However, when the material forming the optical waveguide is a semiconductor or the like, a strong acid may be used for etching the sacrificial layer, and the resist may not withstand the strong acid. Therefore, by providing the thin film heater 6 in the lower clad layer 3, it can be protected from strong acid. As a result, the manufacture of the thermo-optic phase shifter is facilitated and the reliability is improved.
[0072]
Next, a sixth embodiment of the present invention will be described. FIG. 9A is a plan view showing the thermo-optic phase shifter according to the present embodiment, and FIG. 9B is a cross-sectional view taken along line A6-A6 ′ shown in FIG. This embodiment is a combination of the second embodiment and the fifth embodiment described above. That is, as shown in FIGS. 9A and 9B, the support column 2 a made of PSG is provided in the gap 15 between the substrate 1 and the optical waveguide 14. The method for forming the column 2a is the same as in the second embodiment. Further, the configuration and manufacturing method other than those described above in the present embodiment are the same as those in the fifth embodiment described above. In this embodiment, a large mechanical strength can be ensured, and the thin film heater can be protected regardless of the resist when the sacrificial layer is etched.
[0073]
Next, a seventh embodiment of the present invention will be described. FIG. 10A is a plan view showing the thermo-optic phase shifter according to the present embodiment, and FIG. 10B is a cross-sectional view taken along line A7-A7 'shown in FIG. FIGS. 11A to 11D are cross-sectional views showing the manufacturing method of the thermo-optic phase shifter according to this embodiment in the order of steps. This embodiment is a combination of the third embodiment and the fifth embodiment described above. In the fifth embodiment, the sacrificial layer 2 is formed on the entire surface of the substrate 1 and the sacrificial layer 2 and the lower clad layer 3 are continuously formed. In the present embodiment, the third layer described above is used. As in the first embodiment, the sacrificial layer 2 is provided only in the region corresponding to the lower portion of the thin film heater 6.
[0074]
That is, as shown in FIGS. 10A and 10B, in this embodiment, the lower cladding layer 3 of the optical waveguide 14 is separated from the first lower cladding layer 9 and the second lower cladding layer 10. The thin film heater 6 is arrange | positioned between both. The configuration other than the above in the present embodiment is the same as that of the third embodiment described above.
[0075]
Next, a manufacturing method of the thermo-optic phase shifter according to the present embodiment will be described. First, as shown in FIG. 11A, the sacrificial layer 2 is selectively formed on the surface of the substrate 1 as in the third embodiment. Next, as shown in FIG. 11B, the first lower cladding layer 9, the thin film heater 6, and the second lower side are formed on the substrate 1 and the sacrificial layer 2 as in the fifth embodiment. The clad layer 10 and the thin film 4a are formed. Next, as shown in FIG. 11C, the thin film 4 a is patterned to form the core 4, and the upper cladding layer 5 is formed so as to cover the core 4. Next, as shown in FIG. 11 (d), a resist 7 is formed on the upper cladding layer 5, and the upper cladding layer 5 and the lower cladding layer 3 are etched using this resist 7 as a mask to form a groove 8. To do.
[0076]
Next, as shown in FIGS. 10A and 10B, the sacrificial layer 2 is removed by etching through the groove 8 to form a gap 15. Then, electrode vias 11 are formed in the upper cladding layer 5 and the second lower cladding layer 10.
[0077]
In the present embodiment, for the same reason as in the third embodiment, the stress of the sacrificial layer can be released to improve the optical characteristics and the mechanical strength. Further, the thin film heater 6 can be protected during etching for the same reason as in the fifth embodiment.
[0078]
Next, an eighth embodiment of the present invention will be described. FIG. 12A is a plan view showing the thermo-optic phase shifter according to the present embodiment, and FIG. 12B is a sectional view taken along line A8-A8 'shown in FIG. As shown in FIGS. 12A and 12B, this embodiment is a combination of the above-described fourth embodiment and the fifth embodiment. In other words, this embodiment is the above-described embodiment. This embodiment is a combination of the second embodiment and the seventh embodiment. In this embodiment, a part of the sacrificial layer 2 is left in the gap 15 to form the support column 2a made of PSG. The configuration and manufacturing method other than those described above in the present embodiment are the same as those in the seventh embodiment described above. In the present embodiment, the optical characteristics and mechanical strength can be improved, and the thin film heater 6 can be protected during etching.
[0079]
  Next, a ninth embodiment of the present invention will be described. FIG. 13A is a plan view showing the thermo-optic phase shifter according to the present embodiment, FIG. 13B is a sectional view taken along line A9-A9 ′ shown in FIG. 13A, and FIG. It is sectional drawing by the B9-B9 'line shown. FIG. 13 (a)To (c)As shown in FIG. 4, in the thermo-optic phase shifter of this embodiment, the side surface 8a closer to the core 4 among the side surfaces parallel to the longitudinal direction of the groove 8, that is, the direction in which the core 4 extends, is As the end portion 8b is approached, it is curved so as to be away from the core 4. Thereby, the root part 14b in the bridge part 14a of the optical waveguide 14 is thicker than parts other than the root part 14b in the bridge part 14a. Further, in the region corresponding to the lower portion of the root portion 14b in the gap 15, the sacrificial layer 2 remains at the time of etching to form the support column 2a. The configuration other than the above in the present embodiment is the same as that of the first embodiment described above.
[0080]
In the thermo-optic phase shifter according to the first embodiment described above, the mechanically weakest part is the root part 14b of the bridge part 14a of the optical waveguide 14, and it is considered that the mechanical stress is concentrated most in this part. In the present embodiment, the root portion 14b is reinforced by forming a tapered shape. Thereby, the reliability of the thermo-optic phase shifter can be further improved. In order to manufacture the thermo-optic phase shifter according to the present embodiment, the photolithography mask pattern for patterning the resist 7 in the first embodiment described above may be changed. The thermo-optic phase shifter can be fabricated by the self-forming process as in the first embodiment without changing the fabrication process of the thermo-optic phase shifter in the first embodiment.
[0081]
Next, a tenth embodiment of the present invention will be described. FIG. 14A is a plan view showing the thermo-optic phase shifter according to the present embodiment, FIG. 14B is a cross-sectional view taken along line A10-A10 ′ shown in FIG. 14A, and FIG. It is sectional drawing by the B10-B10 'line shown. As shown in FIGS. 14A to 14C, in this embodiment, a beam 16 that supports the optical waveguide 14 with respect to the cladding layer 13 is provided in the middle of the bridge portion 14 a of the optical waveguide 14. . The beam 16 extends in a direction orthogonal to the direction in which the core 4 extends, and is provided so as to stretch the groove 8. The configuration other than the above in the present embodiment is the same as that of the first embodiment described above.
[0082]
In the first embodiment described above, when the bridge portion 14a of the optical waveguide 14 is elongated in the longitudinal direction, the degree of freedom in the lateral direction of the bridge portion 14a, that is, the direction orthogonal to the direction in which the core 4 extends increases. Depending on the case, the optical waveguide 14 may be bent in the middle and propagation loss may increase, or the cladding layer 13 may be in contact with a portion other than the optical waveguide 14 or the substrate 1 to impair the heat insulation.
[0083]
On the other hand, in this embodiment, by providing the beam 16, the degree of freedom in the lateral direction of the bridge portion 14a is reduced. Thereby, when the optical waveguide 14 receives external force, it can prevent that the bridge part 14a bends in a horizontal direction, and the reliability of a thermo-optic phase shifter improves. With such a structure, it is conceivable that the heat insulation is somewhat impaired. However, if the thermal conductivity of the material forming the beam 16 is sufficiently low, the thermal conduction path to the substrate 1 may be long. Yes, it is not a very large heat conduction path. In order to manufacture the thermo-optic phase shifter according to the present embodiment, the photolithography mask pattern for patterning the resist 7 in the first embodiment described above may be changed. The thermo-optic phase shifter can be fabricated by the self-forming process as in the first embodiment without changing the fabrication process of the thermo-optic phase shifter in the first embodiment. The number of beams 16 is not limited to one on the left and right, and a plurality of beams may be provided on the left and right.
[0084]
Next, an eleventh embodiment of the present invention will be described. FIG. 15A is a plan view showing a thermo-optic phase shifter according to the present embodiment, FIG. 15B is a cross-sectional view taken along line A11-A11 ′ shown in FIG. 15A, and FIG. It is sectional drawing by the B11-B11 'line shown. As shown in FIGS. 15A to 15C, in this embodiment, the column 2 a is provided in the gap 15 below the central portion in the longitudinal direction of the bridge portion 14 a of the optical waveguide 14. The support 2a is made of the same material as the sacrificial layer 2 (see FIG. 1D), that is, PSG. The support column 2a is provided on the substrate 1, supports the optical waveguide 14 with respect to the substrate 1, and reduces the degree of freedom in the vertical direction of the bridge portion 14a. In addition, the width | variety 14c equivalent to the upper direction of the support | pillar 2a in the bridge part 14a is larger than the other part.
[0085]
In the first embodiment described above, when the bridge portion 14a of the optical waveguide 14 becomes longer in the longitudinal direction, the degree of freedom in the lateral direction of the bridge portion 14a increases, and in some cases, the optical waveguide 14 bends in the middle. There is a possibility that the propagation loss increases or the heat insulating property is impaired due to contact with the substrate 1.
[0086]
Therefore, in the present embodiment, this can be prevented by providing support columns at appropriate positions. It is conceivable that the heat insulation is impaired by adopting such a structure, but the support column is made of PSG having lower thermal conductivity than the substrate, and the size of the support column is about 10 μm in the vertical and horizontal directions. If so, the heat conductivity is sufficiently low, and the heat conduction path is not so large. Similarly to the ninth and tenth embodiments described above, in order to manufacture the thermo-optic phase shifter according to the present embodiment, photolithography for patterning the resist 7 in the first embodiment described above. The mask pattern may be changed so that a portion 14c having a width wider than other portions is formed in the optical waveguide 14. Thereby, at the time of etching the sacrificial layer 2, the sacrificial layer 2 remains below the portion 14c, and the support column 2a is formed. As described above, in this example, the thermo-optic phase shifter manufacturing process in the first example other than the mask shape is not changed, and the self-forming process is performed in the same manner as in the first example. A phase shifter can be manufactured. In addition, the number of support | pillars 2a is not limited to one, You may provide two or more.
[0087]
Next, a twelfth embodiment of the present invention will be described. FIG. 16A is a plan view showing the thermo-optic phase shifter according to the present embodiment, FIG. 16B is a sectional view taken along line A12-A12 ′ shown in FIG. 16A, and FIG. It is sectional drawing by the B12-B12 'line shown. As shown in FIGS. 16A to 16C, this embodiment is a combination of the tenth embodiment and the eleventh embodiment. In the present embodiment, the beam 16 and the column 2a are provided in the middle of the bridge portion 14a. The configuration and manufacturing method other than those described above in the present embodiment are the same as those in the first embodiment described above.
[0088]
When the thermo-optic phase shifter is used in an environment where the structure of the ninth, tenth, and eleventh embodiments is insufficient in strength, the structure of the present embodiment can be used as a side of the bridge portion 14a. Both the degree of freedom in the direction and the degree of freedom in the vertical direction are reduced, and the strength can be ensured while sacrificing some reduction in power consumption. The change to this structure can be realized only by changing the photolithographic mask pattern used for forming the etching groove, and can be realized by the self-forming process without changing the manufacturing process.
[0089]
Next, a thirteenth embodiment of the present invention is described. FIG. 17A is a plan view showing a thermo-optic phase shifter according to the present embodiment, FIG. 17B is a cross-sectional view taken along line A13-A13 ′ shown in FIG. It is sectional drawing by the B13-B13 'line shown. FIGS. 18A to 18D are cross-sectional views showing the manufacturing method of the thermo-optical phase shifter according to this embodiment in the order of the steps, and FIG. It is a top view which shows the process shown in FIG.18 (c).
[0090]
As shown in FIGS. 17A to 17C, in the thermo-optic phase shifter according to the present embodiment, the support column 12 is formed in a part of the gap 15. The support column 12 is formed of a material having an etching rate larger than that of the sacrificial layer 2 (see FIG. 1D). For example, when the sacrificial layer 2 is formed of PSG, the support column 12 is formed of, for example, BPSG. Yes. The support column 12 is provided in a part in the longitudinal direction of the bridge portion 14a, supports the bridge portion 14a with respect to the substrate 1, and reduces the degree of freedom in the vertical direction.
[0091]
Next, a manufacturing method of the thermo-optic phase shifter according to the present embodiment will be described. First, as shown in FIG. 18A, the sacrificial layer 2 is formed on the substrate 1 by, for example, PSG. Then, a part of the sacrificial layer 2 is removed by photolithography and RIE, and a BPSG film is embedded in the part to form the pillars 12. Next, as shown in FIG. 18B, the lower clad layer 3 and the thin film 4a are formed by the same method as in the first embodiment.
[0092]
Next, as shown in FIGS. 18C and 19, the thin film 4 a is patterned to form the core 4, and the upper cladding layer 5 is formed. Then, as shown in FIG. 18D, a thin film heater 6 is formed on the upper clad layer 5.
[0093]
Next, as shown in FIGS. 17A to 17C, two grooves 8 are formed at positions sandwiching the optical waveguide 14, and the sacrificial layer 2 below the optical waveguide 14 is removed by etching to remove gaps. 15 is formed. At this time, the column 12 made of BPSG remains without being etched. The configuration and manufacturing method other than those described above in the present embodiment are the same as those in the first embodiment described above.
[0094]
As described above, in the eleventh embodiment described above, the pillars are formed by stopping the side etching of the sacrificial layer at a desired time. However, in this embodiment, the sacrificial layer is first etched into a part of the sacrificial layer. In this case, the column portion is made of a material that is not etched at the time. Thereby, for example, when the etching rate of the sacrificial layer is extremely high and it is difficult to stop the etching on the way, the support columns are self-formed, so that the reliability and reproducibility of the manufacturing process can be improved.
[0095]
In each of the above-described embodiments, the case where the optical waveguide is a buried type waveguide has been described. However, the structure of the optical waveguide in the thermo-optic phase shifter of the present invention is not limited to this, and for example, a ridge type waveguide In this case, the effect of the present invention can be sufficiently expected. Further, the shape of the thin film heater is not limited to a single linear shape, and may be a shape obtained by combining a plurality of straight lines or a curved shape, and raises the core of the optical waveguide to a desired temperature. It is only necessary to generate heat that can induce a change in refractive index.
[0096]
【The invention's effect】
As described above in detail, according to the present invention, in the thermo-optic phase shifter, an optical waveguide composed of a core and a cladding layer is formed on a substrate, and a gap of 4 μm or more is provided between the substrate and the optical waveguide. In addition, it is possible to improve the heat insulation properties of the optical waveguide with respect to the substrate, and to obtain a thermo-optic phase shifter having good optical characteristics, strength, stability and reliability and low power consumption. The thermo-optic phase shifter can be easily manufactured by a method generally used in large-scale electronic integrated circuits. For this reason, the present invention is an extremely useful technique for realizing miniaturization, high functionality, and large scale of an optical circuit.
[Brief description of the drawings]
FIG. 1A is a plan view showing a thermo-optic phase shifter according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line A1-A1 ′.
FIGS. 2A to 2D are cross-sectional views showing a method of manufacturing a thermo-optic phase shifter according to the present embodiment in the order of steps.
3A is a plan view showing a thermo-optic phase shifter according to a second embodiment of the present invention, and FIG. 3B is a cross-sectional view taken along line A2-A2 ′.
FIGS. 4A to 4D are cross-sectional views showing a method of manufacturing a thermo-optic phase shifter according to a third embodiment of the present invention in the order of steps. FIGS.
5A is a plan view showing a thermo-optic phase shifter according to the present embodiment, and FIG. 5B is a cross-sectional view taken along line A3-A3 ′.
6A is a plan view showing a thermo-optic phase shifter according to a fourth embodiment of the present invention, and FIG. 6B is a cross-sectional view taken along line A4-A4 ′.
7A is a plan view showing a thermo-optic phase shifter according to a fifth embodiment of the present invention, and FIG. 7B is a cross-sectional view taken along line A5-A5 ′.
FIGS. 8A to 8D are cross-sectional views showing a method of manufacturing a thermo-optic phase shifter according to the present embodiment in the order of steps. FIGS.
9A is a plan view showing a thermo-optic phase shifter according to a sixth embodiment of the present invention, and FIG. 9B is a cross-sectional view taken along line A6-A6 ′.
10A is a plan view showing a thermo-optic phase shifter according to a seventh embodiment of the present invention, and FIG. 10B is a cross-sectional view taken along line A7-A7 '.
FIGS. 11A to 11D are cross-sectional views showing a method of manufacturing a thermo-optic phase shifter according to the present embodiment in the order of steps. FIGS.
12A is a plan view showing a thermo-optic phase shifter according to an eighth embodiment of the present invention, and FIG. 12B is a cross-sectional view taken along line A8-A8 '.
13A is a plan view showing a thermo-optic phase shifter according to a ninth embodiment of the present invention, and FIG. 13B is a cross-sectional view taken along line A9-A9 ′ shown in FIG. (c) is sectional drawing by the B9-B9 'line shown to (a).
14A is a plan view showing a thermo-optic phase shifter according to a tenth embodiment of the present invention, and FIG. 14B is a cross-sectional view taken along line A10-A10 ′ shown in FIG. (c) is sectional drawing by the B10-B10 'line shown to (a).
15A is a plan view showing a thermo-optic phase shifter according to an eleventh embodiment of the present invention, and FIG. 15B is a sectional view taken along line A11-A11 ′ shown in FIG. (c) is sectional drawing by the B11-B11 'line shown to (a).
16A is a plan view showing a thermo-optic phase shifter according to a twelfth embodiment of the present invention, and FIG. 16B is a sectional view taken along line A12-A12 ′ shown in FIG. (c) is sectional drawing by the B12-B12 'line | wire shown to (a).
FIG. 17A is a plan view showing a thermo-optic phase shifter according to a thirteenth embodiment of the present invention, and FIG. 17B is a sectional view taken along line A13-A13 ′ shown in FIG. (c) is sectional drawing by the B13-B13 'line shown to (a).
18A to 18D are cross-sectional views showing a method of manufacturing a thermo-optic phase shifter according to the present embodiment in the order of steps.
FIG. 19 is a plan view showing the step shown in FIG. 18C in the manufacturing method of the thermo-optic phase shifter according to the embodiment.
[Explanation of symbols]
1; substrate
2; Sacrificial layer
2a; support
3; Lower cladding layer
4; Core
4a; thin film
5: Upper cladding layer
6; Thin film heater
6a; electrode part
6b: Heater part
7; resist
7a; opening
8; Groove
8a; side
8b; end
9: First lower cladding layer
10; second lower cladding layer
11: Via
12; strut
13: Clad layer
14: Optical waveguide
14a: Bridge-shaped part
14b; root
14c; part
15; gap
16; Beam

Claims (27)

A substrate, a sacrificial layer provided on the substrate, a clad layer provided on the sacrificial layer, a core provided in a straight line or a curved line in the clad layer and constituting an optical waveguide, and immediately above the core A heater provided in a region including a region or a region directly underneath to change the phase of light of the optical waveguide by generating heat, and a groove in a region sandwiching at least the region directly under the heater in the sacrificial layer and the cladding layer The thermo-optic phase shifter is characterized in that the sacrificial layer sandwiched between the grooves is removed to form a gap of 4 μm or more connected to the grooves.   2. The support portion according to claim 1, further comprising a column portion that is locally provided in a part of the gap in a direction in which the core extends and supports a portion between the grooves in the cladding layer with respect to the substrate. Thermo-optic phase shifter.   A substrate, a sacrificial layer formed on the substrate and formed by a sacrificial material having a higher etching rate than the material forming the substrate, and a material provided on the sacrificial layer and having a lower etching rate than the sacrificial material The clad layer formed in the clad layer in a straight line or a curved line and constituting an optical waveguide, and provided in a region including a region directly above or directly below the core to generate heat, thereby generating light of the optical waveguide. And a groove is formed in a region sandwiching at least a region immediately below the heater in the sacrificial layer and the clad layer, and the sacrificial layer sandwiched between the grooves is removed by etching. A gap connected to the groove between the portion of the cladding layer between the groove and the substrate, and a part of the gap in a direction in which the core extends. Parts manner provided, the thermal optical phase shifter characterized in that it has a support portion for supporting the cladding layer portion sandwiched between the grooves with respect to the substrate.   The thermo-optic phase shifter according to claim 3, wherein the support portion is made of the sacrificial material.   The thermo-optic phase shifter according to claim 3, wherein the support portion is made of a material having an etching rate smaller than that of the sacrificial material.   6. The thermo-optic phase shifter according to claim 3, wherein the thermal conductivity of the sacrificial material is smaller than the thermal conductivity of the material forming the substrate.   7. The thermo-optical phase according to claim 3, wherein the sacrificial material is a glass material containing phosphorus, and the material forming the cladding layer is a glass material containing boron and phosphorus. Shifter.   The thermo-optic phase shifter according to claim 3, wherein the gap is 4 μm or more.   The thermo-optic phase shifter according to any one of claims 2 and 3 to 5, wherein the support portion is formed in a part of a direction in which the core extends. In the portion between the grooves in the cladding layer, the width of the cross section that includes the region directly above the support column and orthogonal to the direction in which the core extends is equal to the width of the cross section that does not include the region directly above the support column and orthogonal to the direction in which the core extends. The thermo-optic phase shifter according to claim 9 , wherein the thermo-optic phase shifter is larger than the thermo-optic phase shifter. Provided to tension said groove, a portion between the grooves in the cladding layer, of claims 1 to 10, characterized in that it has a support beam for supporting against the portion sandwiching the groove with this part The thermo-optic phase shifter according to any one of claims. Of the side surfaces parallel to the direction in which the core extends in the groove, the side surface closer to the core is curved so as to move away from the core as it approaches the edge in the direction at the end in the direction in which the core extends. thermo-optic phase shifter according to any one of claims 1 to 11, characterized in that there. Thermo-optic phase shifter according to any one of claims 1 to 12, characterized in that the heater is provided on a surface of the clad layer. Thermo-optic phase shifter according to any one of claims 1 to 12, characterized in that the heater is provided in the cladding layer. The thermo-optic phase shifter according to any one of claims 1 to 14 , wherein the core and the cladding layer are made of a glass material containing quartz. The thermo-optic phase shifter according to claim 15 , wherein the glass material forming the core contains germanium. The thermo-optic phase shifter according to any one of claims 1 to 16 , wherein the substrate is made of a glass material containing quartz or silicon.   Forming a sacrificial layer on the substrate with a sacrificial material having an etching rate higher than that of the material forming the substrate, and forming a lower clad layer on the sacrificial layer with a material having an etching rate lower than that of the sacrificial material. And forming a linear or curved core on the lower cladding layer, forming an upper cladding layer with a material having an etching rate smaller than that of the sacrificial material so as to cover the core, Forming a heater that changes the phase of light in the optical waveguide composed of the lower clad layer, the core, and the upper clad layer by generating heat in a region including the region directly above the core on the clad layer; and the upper clad layer And forming a groove reaching the sacrificial layer or the substrate in a region sandwiching a region directly below the heater in the lower clad layer, and The sacrificial layer located between the substrate and the portion between the groove in the lower cladding layer is removed by etching, and between the portion between the groove and the substrate in the lower cladding layer In addition to forming a gap connected to the groove, a support column part is provided locally to support the clad layer portion sandwiched by the groove with respect to the substrate in a part of the gap in a direction in which the core extends. And a process for producing a thermo-optic phase shifter.   Forming a sacrificial layer on the substrate with a sacrificial material having an etching rate higher than that of the material forming the substrate; and forming a first lower cladding layer on the sacrificial layer with a material having an etching rate lower than that of the sacrificial material. Forming a heater on the first lower cladding layer, forming a second lower cladding layer on the heater with a material having an etching rate smaller than that of the sacrificial material, Forming a core extending linearly or in a curved line in a region including the region directly above the heater on the second lower cladding layer, and covering the core with a material having an etching rate lower than that of the sacrificial material. A step of forming a cladding layer; and a region directly above the heater in the upper cladding layer and the second lower cladding layer and the first lower cladding layer. Forming a groove reaching the sacrificial layer or the substrate in a region sandwiching a region directly below the heater, and a portion between the groove and the substrate in the first lower cladding layer via the groove Etching and removing the sacrificial layer located on the first clad layer, and forming a gap connected to the trench between the substrate and the portion between the trench in the first lower clad layer, and the upper clad Forming a via connected to the heater in the layer and the second lower cladding layer. A method of manufacturing a thermo-optic phase shifter, comprising: 20. The method of manufacturing a thermo-optic phase shifter according to claim 18, wherein the thickness of the sacrificial layer is 4 [mu] m or more.   A step of selectively forming a sacrificial layer having a thickness of 4 μm or more on a substrate with a sacrificial material having an etching rate higher than that of the material forming the substrate, and a material having an etching rate lower than that of the sacrificial material on the sacrificial layer A step of forming a lower clad layer, a step of forming a core extending linearly or in a curved line in a region including an upper region of the sacrificial layer on the lower clad layer, and the sacrificial material so as to cover the core Forming an upper clad layer with a material having a lower etching rate than the above, and generating light in a region including the region directly above the core on the upper clad layer, thereby forming an optical beam composed of the lower clad layer, the core, and the upper clad layer. A step of forming a heater that changes the phase of light in the waveguide, and a region immediately below the heater in the upper cladding layer and the lower cladding layer. Forming a groove reaching the sacrificial layer or the substrate in a region, etching the sacrificial layer through the groove, and removing the sacrificial layer between the portion of the lower clad layer and the substrate A strut portion that forms a gap of 4 μm or more connected to the groove and supports the clad layer portion sandwiched by the groove to a part of the gap in a direction in which the core extends is locally provided. A method of manufacturing a thermo-optic phase shifter.   A step of selectively forming a sacrificial layer having a thickness of 4 μm or more on a substrate with a sacrificial material having an etching rate higher than that of the material forming the substrate, and a material having an etching rate lower than that of the sacrificial material on the sacrificial layer A step of forming a first lower cladding layer, a step of forming a heater in a region on the first lower cladding layer including a region immediately above the sacrificial layer, and the sacrificial material on the heater. Forming a second lower cladding layer with a material having a low etching rate, and forming a core extending linearly or in a curved line in a region including the region directly above the heater on the second lower cladding layer; A step of forming an upper clad layer with a material whose etching rate is lower than that of the sacrificial material so as to cover the core, and the upper clad layer and the second lower clad layer Forming a groove reaching the sacrificial layer or the substrate in a region directly above the heater and a region directly below the heater in the first lower cladding layer, and etching the sacrificial layer through the groove Forming a gap of 4 μm or more connected to the groove between the substrate and the portion between the grooves in the first lower cladding layer, and removing the upper cladding layer and the second cladding layer. Forming a via connected to the heater in a lower clad layer, and a method of manufacturing a thermo-optic phase shifter. In the step of etching the sacrificial layer, a part of the sacrificial layer located between the core and the substrate is locally left in a part in a direction in which the core extends, whereby the lower clad layer The method of manufacturing a thermo-optic phase shifter according to claim 19 or 22 , wherein a support portion that supports a portion between the grooves with respect to the substrate is formed. The thermo-optic according to claim 18 or 21 , wherein at least one of the sacrificial layer, the lower cladding layer, the core, and the upper cladding layer is formed by an atmospheric pressure chemical vapor deposition method. Manufacturing method of phase shifter. At least one of the sacrificial layer, the first lower cladding layer, the second lower cladding layer, the core, and the upper cladding layer is formed by an atmospheric pressure chemical vapor deposition method. The method for producing a thermo-optic phase shifter according to claim 19 or 22 . 26. The method of manufacturing a thermo-optic phase shifter according to claim 18, wherein in the step of etching the sacrificial layer, the sacrificial layer is etched with a buffered hydrogen fluoride solution. When forming the groove, the width of the sacrificial layer in the cross section that includes the region directly above the support column and orthogonal to the direction in which the core extends is set to By making the width larger than the width of the sacrificial layer, in the step of etching the sacrificial layer, a difference is partially caused in the time until the etching step is completed, and the support column is formed locally. The manufacturing method of the thermo-optic phase shifter of any one of Claims 18 thru | or 26 .

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